The electrical characteristics of low-k dielectric materials make them desirable in the manufacture of semiconductor chips having sub micron features. Low-k dielectric materials include such commercial products as Dow Corning's SILK™ and porous SILK™, Applied Materials' Black Diamond™, Motorola's Black Diamond™, Texas Instrument's Coral™, and TSMC's Black Diamond™ and Coral™ and other organic polymers, porous oxides and carbon-doped oxides as described below. In one particular application of interest with respect to the present invention, these low-k dielectric materials are used to insulate sub-micron copper interconnects. The electrical characteristics of these low-k materials diminish the capacitive effects between the closely spaced electrical conductors. Such conductors include, for example, dual damascence-formed copper conductors used to make back-end-of-ine (BEOL), multilevel electrical connections to silicon devices such as transistors.
These low-k dielectric materials, however, possess certain chemical and mechanical characteristics that make them problematic for certain applications. They are, for example, soft, pliable and porous as well as prone to electrical leakage. These characteristics make it difficult to probe rough these materials to test the electrical characteristics of the underlying components. Processes typically used to open vias through the low-k dielectric materials, such as mechanical unlayering, reactive ion etching (RIE), focused ion beam (FIB) techniques and wet chemical removal processes either compromise the underlying structures to be tested or cause conductive leakage paths within the dielectric layers themselves, compromising sensitive electrical measurements.
It thus is difficult to electrically probe and analyze the electrical operating characteristics or fault characteristics of semiconductor devices fabricated using these low-k dielectric materials.